Background
Smartphones are a ubiquitous part of modern day life. However, when used to listen to music in large rooms (eg festive music in operating theatres), the low volume is a significant limiting factor to enjoyment. We have observed that a size 5 adult facemask may be employed to produce a subjective increase in volume from smartphone speakers.
Technique
Once the optimum position for the smartphone within the facemask was identified (Fig 1), a series of experiments were carried out to compare the frequency responses from unmodified and modified smartphones using 34 standard audio test tones ranging from 16Hz to 20kHz (Bink Audio Test CD; HEAnet, Dublin, Ireland). These were measured with a sound pressure level meter application (Decibel 10th; SkyPaw). The modification caused a shift in the resonant frequency from 4kHz to 1.25kHz, with a 10dB gain around 1.25kHz (Fig 2). Further analysis with an audio spectrum analyser application (RTA Lite; Studio Six Digital) showed that the majority of festive tunes, including Merry Christmas Everybody by Slade, produced signals centred around 1.25kHz, with a range of 250Hz to 8kHz.
Figure 1.
Smartphone with improvised amplification device. Acoustic effects of the decorative sprigs of holly are unknown
Figure 2.
Frequency response curves at 40cm for smartphone loudspeakers with and without improvised amplification device
Discussion
The facemask achieves the subjective increase in volume by acting as a substantially parabolic reflector and/or Helmholtz resonator, optimising the output of the smartphone to approximately the centre of the tonal range for male voice and guitars. 1 We therefore propose that a size 5 facemask may be employed as an improvised amplifier to enhance enjoyment of festive music.
Reference
- 1.Sen SN. Acoustics: Waves and Oscillations. New York: Wiley; 1991. [Google Scholar]